Image formation and development



June 30, 1970 K ET AL 3,518,081

IMAGE FORMATIOI I AND DEVELOPMENT Filed Feb. 7. 1964 IMAGE WISETRIBOELECTRIC MODIFICATION CHARGE BY FRICTiONAL CONTACT DEVELOP IN VENTOR.

WILLIAM L. GOF'F'E JOHN KMORE BYJ%%BQ(QQQ ATTORNEY 6f'electrostatography.

n te-d ees P ABSTRACT on THE DISCLOSURE 1 Graphic reproductions areachieved by the image-wise modification of the triboelectric chargingcapability of a surface followed by the triboelectric charging of themodified surface to produce a charge pattern corresponding to an image;The charge pattern may be developed with finely divided coloredelectroscopic particles and the resulting colored image either fixed onthe surface of the insulating member or transferred to a receivingsurface and fixed thereon. V

This invention relates in general to electrostatography "andmoreparticularly to a new method for the reproduction of' images basedon the imagewise modification of the-triboelectric charging capabilityof a surface.

"Electrostatography encompasses the entire field of forming andutilizing latent electrostatic charge patterns to record and reproduceimages in visible form. The field of electrostatography was pioneered byChester F. Carlson when he disclosed in US. Pat. 2,297,691 the basictechnique of one major sector of the electrostatographic field referredto as xerography. In the most commonly practiced form of xerography, aphotoconductive insulating layer is first given a uniform electrostaticcharge over its entire surface and is thenexposed to an image ofactivating electromagnetic radiation such as light which selectivelydissipat'es the charge in illuminated areas of the photoconductiveinsulator, while charges in the non- -il1uminated areas are retained,thus forming a latent electrostatic imaige. This latent image may thenbe developed or made' visible by the deposition of finely dividedcolored electroscopic marking particles on the surface of the'photoconductive insulating layer, as a result of which-the markiiig'particles adhere to the surface of the photoconductive insulating layeronly in areas of retained charge. This developed image may then beutilized, in a number of diverse ways. For example, the imagefimay beviewed in sitii on the photoconductive insulator, fixed 'in placeon itssurface or transferred to a second surface "suchas'a sheet of paper'and'fixed thereon as desired, depending upon whether the'photoconductive insulating layer is reusable the process or not.Hundreds of additional patents have issued in the'field of xerographysince the time of the original Carlsonpatents incorporating manyimprovements and modifications into the basic process and as a result ofthis development, xerography is 'today; by a greatmargin the largestcommercial sector The other broad general branchof electrostatography.r. eiierally-referred to'as electrofgraphy and it is contloesi notemploy a photoconductorand light exposure to control" the formation ofits "latent electrostatic charge pattern; Electrography 3 as it is"generally known' today l rriay be'divided into two broad 'sectors whichare, xeroa 12 Claims sidered"distinct'fromthexerographic'branch in thatit 3,518,081 Patented June 30, 187i) ice stemming from thephraseTransfer of Electrostatic Images) the electrostatic charge.v patternsconforming to the desired reproduction are formed on a uniforminsulating layer by means of an electrical discharge between two or moreelectrodes on opposite sides of the insulating medium. By controllingthe shapes, combinationsand numbers of electrodes employed, chargepatterns of almost any shape may be formed on the insulating material.In both xeroprinting and TESI recording, image development is by thesame techniques employed in xerography.

The common feature of all of these electrostatographic systems is thatthey employ the lines of force from the electric field of a latentelectrostatic image to control the deposition of the colored finelydlivided marking particles known as toner, thus forming a visible imagecorresponding to the charge pattern.

Now in accordance with the present invention there is provided a newmethod of forming a latent electrostatic image and an improvedelectrostatographic process in which reproduction is formed by theimagewise modification of the triboelectric charging capability of aninsulating surface followed by triboelectric charging of the modifiedsurface to produce a charge pattern corresponding to the image, andoptionally development of the charge pattern with finely divided coloredelectroscopic particles and alternatively fixing the particles on thesurface of the insulating member or transferring the particles toanother copy surface and fixing thereon.

The above and still further features, objects, and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed disclosure of specific embodiments of the inventionespecially when taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is a flow sheet of the process steps of the invention.

FIG. L2 is a side-sectional view of an apparatus employing one of theprocess embodiments of the present invention.

Referring now to FIG. 1, it is seen that the first step of the processconsists of modifying the surface of the layer upon which the image isto beforrned in imagewise configuration so that areas of this surfacewhich correspond to the image to be reproduced differ significantly intheir triboelectric charging capabilities from the remainder of thissurface. By way of background, it should be noted at this point thatmany materials may be charged by triboelectrification, that is to say,by rubbing them together with another material. Various materials havebeen arranged into a sequence knownas the triboelectric series which-isso arranged that any one of the materials is positively electrified orcharged by rubbing it with any other material below it in the sequence.

Conversely, any material in the triboelectric series may suchelectrification is governedlby the distance between the materialpositions in the triboelectric series, that is to say, the greater thedistance they arefremoved'from one another in the series,' the greaterthe mutual electrification or charging and the closertogether they arein' the series, the less the mutual electrification o'r' charging. The

present invention thus contemplates modifying allthe imageareas' or allthe non-image areas of a surface upon which the image is to be formed soas to change the'posi- -tion of these modified areas in thetriboelectric series with respect tothe remainder of the imagingsurface. "this sway, .whenihejmagingsurfaceis. rubbervw-ith amaterial arange -0f-visible alightthey generally still remain -most which isdistant in the triboelectric series from either the image or non-imageareas, from this surface a differential charge pattern" or latentelectrostatic image is. formed von hi aains sgrfac'el v I if T is latentelectrostatic image .rnay then be used ina number. 9f. ways. Forexample, it, maybe read-out .by ieleetrostatie chargesensing as with anelectrometer for ,direct. use or radio transmission to a distant pointor. it ,may be made visibleby any, one of a number of wellltnowntdeveloping te chniquesva s described hereinafter, .Ihe d erential-in .triboelectricalcharging susceptibility. of ge ornon-ijmag e. .areasj of vthe surface upon which the number of different techniques whichare explained in greater detailiin the examples given below. Thesetechniques, however, may generally be grouped into two categories whichare (1) charing the triboelectric charg- .ing susceptibility of theimaging surface itself in imagewise configuration or (2) coating theimaging surface in imagewise configuration with a thin layer of a secondmaterial remote from it in the triboelectric series. With eithertechnique the object is to end up with either image or non-image areashaving a position in the triboelectric series which is remote from theposition in the triboelectric series of the material which is rubbedagainst the surface to charge it while other areas of the surface have asub- ,stantially different position in the triboelectric series withrespect to this charging material.

In one of the exemplary techniques described below in the examples, thetriboelectric charging susceptibility of the imaging surface is itself,modified by employing a polymerizable material as the image formingmaterial and polymerizing or crosslinking the material in imageconfiguration by photographic exposure where the material is.photopolymerizable or by imagewise selective heating where the monomercan be polymerized (or a polymeric material can be crosslinked) byheating. This technique achieves the desired results because the polymeror crosslinked polymer has a different triboelectric chargingsusceptibility than the monomer or non-crosslinked poly- .rner fromwhich it is formed and the more highly polymerized the material is, thegreater is this difference in triboelectric charging susceptibility.Since polymerization from a simple monomer and crosslinking of alreadyformed polymeric units both serve to increase the molec- -ular weight ofthe material acted upon, the verb reproduction .is to be formed may beestablishedby a 'polymerize and the noun polymer shall be used.generically to includeboth of these concepts. Because triboelectriccharging is based on a surface phenomenon, it is only necessary tomodify a very thin layer of the surface of the imaging surface in orderto achieve the desired results and this rule applies equally tomodification of the material itself or to imagewise coating of thematerial as described above. Accordingly, it is only necessary topolymerize or crosslink a very thin surface layer of the material toachieve the desired results and polymerizationor crosslinking throughoutthe bulkof the layer is unnecessary although it does not detract fromthe results. inany' way. =-Thisisqmost important since, with mostphotopolymerizablematerials, electromagnetic radi- {ation in;v theultraviolet range is required to cause, photog-polymerizatipmandthegreatest part'of this radiation is -of' instant invention- -onlyrequires surface polymaerizat-ion,it'imrnediately becomes apparent thatthis sys- .-tem has" a faster effectivephotographic speed thanothertimaging-systems based on photopolymerizationwhich reiqlet whiehpenetrates, into the layer. Since-the process iquire. polymerizationthroughout the bulk of their imaging layers. Eventhoughmany;photopolymerizable systems may be sensitized to electromagneticradiation in the electroscopic, colored marking :particleg,

of this :type generally; range, in, size from ab microns with averageparticle sizes from,abou

-.electric ally insulating, the moplastieresins; hpwever, .of -the--con;ventional deye oping ;-materia s.. .u sed ,in, v xerosensitive toUV light.

The fact that modification of only a thin surface layer of the imageforming material is required in the process of the instant inyention'i's falsiiadvantageous in thetechniqiie "where surface eoatin'gsareemployed {detect this change in imagewise configuration,- sin:e'verjy=thin layers of these co'atingsranging tofmonorn c'u'lar '1n- 1cness may be effectively employedf-ln' fact, t-h ese layers may be sothin that theyfma-y bethought of as almost surface ;coj nt a m inantlayers. These contaminants;,may eithefibe inert to, or reactive with theimaging surface. In fact, the contaminant "may 'evea'tea catalyst oroxidizing agent for 'examplewhich serves to increase. the/molecularweight of the surface it contacts as.by-ordinaryiaddition orcondensation polymerization of thepsurfac e orby oxy gen bridgingpolymerization of unsaturated molecules (this latter mechanismisbelieved to bethe .one respon sible for the hardening 'of the dryingoils).

Once the modification .of .triboelectric echarging stlsceptibility ofthe image forming surface has.been accomplished in imagewiseconfiguration, the surfaceyistribo: electrically charged byuniformfrictional c onta et with a charging member. This charging may beaccomplished by rubbing with glass,-rubber,-fur, metals, wool, otherfabric or any other material selected according-dons;position in thetriboelectric series with. respect ,to the position in that series ofimage and. non-image ,areasoffl-the image forming layer so as to effectthe desired chargingpattern. Friction charging can also be acliieyedbythe-,flow, of a liquid or gas past thestlrfaceto,belcharged,,-Inaddition to rubbing the surface to. becharged. witht one' ofthematerials listed above, charging maybe accomplished by cascading smallbeads of the material over-the.,surfac e to be charged. This techniquemay employ. coated carrier beads of the type described in U.S. Pat. 2,6-18,55'1 to Walkup, and depending upon the material employed for thesurface coating of the heads, a positive or negative image may beformed. N a

In the following examples beads are referred to, as type A where theposition of their coatings in the.triboelectric series is suchthat theywill charge most materialswhich they rub against negatively and as typeB where theywill charge these materials positively. Typical ,type A -beads are described in detail in Examples 4-7 of U.S;.Pa,t. 2,618,551 andtypical type B beads are described in Examples 1-3 of that patent. Imageand non-image areas of the imaging surface may be on opposite sides ofthe charging material in the triboelectric series so that the chargingmaterial charges one positively and the ,other'negatively, or, in thealternative both types of areasrnay-be on one side of the chargingmaterial in the triboelectric series but separated from each other sothat, for, example, the

charging material may render image areasmqrepositive than non-imageareas or more negative than non-image areas. Thus, image areas canbecharged to6 00..vol,ts,positive while non-image areas are chargedto;300yoltspositive by the triboelectric charging of thefrictionehargingmaterial.

. cally charged by frictional contactyviththe.clnirgingrnates t image bi i t e i sl ee ftt rial, thus forming a latent electrostaticchargepattern, s. charge p nmar .e a z lee-bs ds s s or -r i e ed p si ia he o rof-finel m s ed, w xix-th electrostatographic artv as fitQn 10microns and in most gcases, are ,ma de up of pigmented,

graphy may be employed to develop the latent electrostatic: image formedby the method described above. Reference is hereby made to U.S. patents,Re. No. 25,136 to Carlson; 2,891,001 to Insalaco; 3,079,342 to Insalaco;21659 ;679' to C6pley'.and2',788,288' to Rheinfrank et al. for a moredetailed disclosure of these toners. The develbring nress...('as.distingu hedtromt e evelop material or toner itself) may beaccomplished using any one of a number of, Well .known xerographicdeveloping techniques such as brush development as described in U.S.2,975,578 to 'Byrd, powder cloud development as described "in-U.S.2,918,900 to Carlson, skid development as described in U.S. Pat.2,895,847 to Mayo or immersion development wherein the toner particlesare suspended inan insulating liquid as describedin U.S. Pat. 3,010,842to Ricker. Another development technique which may be employed. isrthecascade development technique which is, today, perhaps the most widelycommercially used xerographic development technique. This developmenttechnique which is more fully described in U.S. Pat. 2,618,552 and 2,638,416 utilizesatwo element developing mixture including the finelydivided toner particles and grossly larger carriergbeads of the sametype as the coated beads described above for frictionally charging theimaging surface. These carrier beads serve bothto maintain the finetoner particles deagglomerated and to charge them by virtue; of therelativerpositionof the toner and carrier materials in'thetriboelectricseries and the constant rubbing together of these materials as thedeveloping mixture-is conveyed through the developing system. Since thecarrier. beads and toner particles tend to charge each other. ,toopposite polarity the carrier .beads collect the toner particles ontheir surfaces and carry them through the developing apparatus. Whenthis mixture is cascaded over the' surface bearing the .latentelectrostatic image, theyelectrostatimfield from the charge patternremoves the toner particles from the carrier beadsbecause itselectrostatic attraction for the toner particles is stronger than thatof-the .carrier beads in charged areas, Once the developing-mixture ?hascascaded over the surface to be developed, the carrier beads along withany toner particles not employed in the development fall back into thebottom ,of an 'adjacent container for later recirculating in thedeveloping process. Wherever this developer-is recirculated;as'described above,toner particles in the mixture arerrreplenishedperiodically; It isalso possible to combine charging and developmentwithrthis and other types of v developers where the developerisin'frictional contact with the imaging surface during development,however, development usually takesa longer time with this. combinedtechnique-because there is no charge on the irnaging surface when thedeveloper first contacts it. Elhistechnique has been experimentallyproven with good results.., I i 1 r Afterthe latentelectrostaticirnagehasbeen developed, it maybe either transferred to "another'surface as bybringing ithetoner'particle image'into contact with an adhesive web orit may b'etransferred to an insulating web-by electrostatic transfer asdescribed in U.S. Pat". 2,576,047- to Sc-haired; In the event that thetoner particle image is'not transferred to an' adhesive surface, it isgen wally-perma ently attached to either the surfac :npon which it wasoriginally formed or the 's urface to which it"ist'ransferred-by fixing;This fixing may beaccomplished by: heating the toner particles to"'fusethem to their substrate when 'they are thermoplastic in nature or by sulr them'iwitli an adhesive material. lrl-additiori td d'e velop i'r'lg'the' lateiiit electi'ostatic image, as described "above, the image-"may"be fre'ad out' by a sfca'iining device capable of sensi g'the chargelever in sequential image areas or ;it

6 and then softening the surfaceuntilthe electrical ,field forces of theelectrostatic image exceed the surface ten: sion forces of the surface.Transfer of electrostatic images from one surface to another isdescribed in Walkup Pat,

may'bereridfered: visiblebyw techniques'such as charge indtieed plasticdeformationf Thia latter technique inf volves forrriirigfth latentelectrostatic image one surface ii capable' oflfornfiiiig' a plasticdeformation image ortransferring: the electrostatic image to such a:surface No. 2,833,648. An exemplary process of plastic'deformai tionimaging is described in more detail in U.S. patent application, Ser. No.193,277, filed May 8, 1962, now Pat. No. 3,196,011. I The process of theinvention was carried out inanumber of experiments as described in thefollowing examples: In all examples the same toner which is described indetail in U.S. Pat. 3,079,342 to. Insalacowas used both for a positivelyand a negatively charged developing material, only different types ofcarrier beads were used,

as described above, to charge the toner particles. tor' differentpolarities.

All exposures to ultraviolet light in the examples were one minuteexposures with, a .Hanovia high pressure mercury arc lamp of watts.

EXAMPLE I A 1.5 mil biaxially oriented (1,4-bis methyl cyclohexariepolyterephthalate) and available from the Eastman Kodak Cc'un'p'anyofRochester, New York under the traden'ame of ."Ko dai" was laid down on asupport ,a'nda persons finger was brought into contact with the surfaceof .thelfilr'll j bl ali ently leaving behindasurface]lcontamination'of'body oils in the form-of a finger print.Thefilm was then friction charged by icascading'a number 'of type I Bcoated carrier beads across the surface of the Kodar and was developedwi'thpositively charged developer-according to the cascade developmenttechnique as described above; This developed the areas of the-Kodar towhich body oils had been'trans ferred'while'the 'use of negativelycharged developer produced development in background L I z AM EIL. 4 rr.

A 1.5 mil Kodar film was'coated'with' a thin layer of KPR(Kodak"'Photoresist availa'ble'fromdh e Eastman Kodak Company ofRochester, New-York). KPR may be describedchemic'ally as the cinnamateesters ofp'oly' vinyl alcohol and of celluloser'zThis "polymer containsunsaturated side groups which may be caused to cro'ss link upon exposureto form very large insoluble molecules and may be further sensitized bythe presence of anthrones and their derivatives, polynuclearquinacridone derivatives and. certain ketones; such as;Michlersketoneasmore .u y d s d: n las-11 70 285; $61 2 6 and 2 6 2 -i 1; 1 M a k t aThe KPR fi m. s d ed n e o o a i h '1 .&t a -.-Qr' hd n Q theimaget0bereprodueed-With alight, source rich .in avi et sites lte n th e sslnk ns annt r age t i ql b li neisfthe KPR.' PQ :araf ewr ing exposurethe KPR was washed with a trichloro ethylene solvent to remove the KPRin unexposedar eas and allowed to dryrjThi s-r esulted-in.a-Kodar filmcoated with KPR in exposed areas. The film surface was then frictioncharged by cascading type B coated charging beads over 'its errate.This-"served to charge KPR): coated areas jmor 1 positive than theKoaar' bs rgrpuna 'areas: When a negatively charged developing material(cascade type) was applied to this "surface, KPR"coated areas w I 'edeveloped and when a positively charged developer was used, the uncoatedKodar areas were developed. Both types of development produced goodimages. This experiment was also successfully repeated using apolyethylene terephthalate substrate in place of the Kodar film.

EXAMPLE III A thin layer of KPR was coated on the surface of asupporting substrate and exposed in the same manner as described inExample II, except that unexposed surface areas of the KPR were notetched away with an organic solvent but instead the complete KPR surfaceincluding both exposed, crosslinked areas of the KPR and nonexposedareas were friction charged with type B coated charging beads which madeunexposed areas more positive than exposed areas. Application of anegatively charged cascade developing material developed unexposed KPRareas.

EXAMPLE IV A 1.5 mil Kodar film was laid over a printed page from a bookand then exposed to a strobe light flash through the Kodar of sufficientintensity to cause the more volatile components of the ink to volatilizeand evaporate across to the Kodar surface in the configuration of theprinted copy. This coated Kodar was then friction charged with coatedcharging beads and developed with a cascade developing material asdescribed in Example I with the same results.

EXAMPLES V-VIII Four imaging surfaces were prepared exactly inaccordance with the provisions of Examples I-IV except that instead ofcharging the surfaces which coated charging beads described in thoseexamples, each of the surfaces was charged by rubbing it with a viscoserayon, long fibered, cotton-like material and was developed by cascadedevelopment as described above. Good quality positive and negative tonerimages of generally higher contrast were produced depending upon thepolarity of the developer.

EXAMPLES lX-XII of polymethyl methacrylate and on a 1.5 mil thick sheetof polyethylene terephthalate available from E. I. du Pont and Companyunder the tradenarne Mylar. These materials produced images of about thesame quality as the imagesformed with the Kodar film utilized in'Examplesl a i f f Sa mplesof aIL S miljKodar film, a-Mylar brandpolyethylene terephthalate film and a Lucite brandpolymethylmethacrylate film were exposed to images with UV light. When thesefilms-were triboelectrically charged by rubbing with various materialsthere was a distinct difference in the charge on exposed and unexposedareas as indicated in the table below: 1

Good quality positive and negative (photographically) images weredeveloped on all surfaces after rubbing,'with the type of imagedepending upon the polarity of'the toner employed in development.

Additional experiments were run on KPR films to deter mine how exposurechanges the films charging ability with different amounts of rubbingwith rayon. It was found that a straight line relationship existsbetween the voltage on exposed film areas and voltage on unexposed filmareas with each point plotted for increasing amounts of rubbing. Theline was found to start at (0, 0) with no rubbing and run through apoint equal to 2000 volts for exposed areas and 3000 volts for unexposedareas.

It is to be noted that the examples given above are exemplary only andare in no way intended to be limiting upon the invention since manyother alternative materials and techniques which now become obvious maybe substituted for the specific materials employed in the exam ples.Thus, for example, instead of charging a polymethyl methacrylate layerby rubbing it with a viscose rayon it may be charged by rubbing with amaterial even more remote from it than rayon in the triboelectric seriessuch as rubber or polyethylene. In addition, a surface contaminant maybe transferred to the imaging sheet through a stencil or by pressing itagainst a printed or typed page with heat and/or pressure, by directlytyping or printing the contaminant on the image forming surface, byelectrostatic transfer or by other techniques with or withoutintermediate transfer. I

Referring now to FIG. 2 there is shown a copying apparatus embodying theconcept of this invention in which the imaging surface 11 is fed up froma supply roll 12 around idle rollers 13 and 14 to a take-up roll 16, inthe meantime passing the process stations of the apparatus. In thisparticular instance, the imaging surface 11 consists of a substratelayer coated with a thin coating of KPR as described above. As theimaging surface begins its movemeut through its path of travel in theapparatus, it passes a projector 17 which projects a light image of theoriginal to be reproduced on the imaging surface with light which isrich in ultraviolet. This projector may either employ a flash exposurewith light of sufiicient intensity to crosslink exposed portions of theKPR layer on the imaging surface 11 as it moves past the projector or inthe alternative, a weaker light source may be employed providing thatthe imaging surface is stopped opposite the projector at intervals toallow for a longer exposure. Once the imaging surface 11 has beenexposed, it continues on in its path of movement until it comes oppositea triboelectric charging roller 18 which serves to charge the imagingsurface producing a differential charge pattern on it as described abovein connection with the examples. This charging roller preferably rotatesin a direction such that its periphery moves opposite the direction ofmovement of the imaging surface and at a speed sufficient to impart asignificant charge to the imaging surface. Actually, the direction ofrotation is not critical so long as the roller 18 may have a surfacecoating of any of the materials described above such as viscose rayon,nylon, wool or the like. This frictional rubbing serves to form adifferential charge pattern on exposed and unexposedareas of the KPRlayer as described in Example HI above. Once charging has beencompleted, the imaging web continues on, moving past a cascadedeveloping unit generally desig-, nated 19. The cascade unit includes anouter container or cover 21 with a trough at its bottorn containing asupply ofthe two component developing material 22. Thisdevelopingmaterial is picked up from thebottom of the trough and dumped orcascaded over the surface of the imaging web 11 by a number of buckets23 on an endless driven conveyor belt 24 which rotates about two pulleys26. As stated above, the cascade development technique is more fullydescribed in U. S;j Pat 2,618,552 and utilizes amixture includingfinely" divided, colored toner particles, and grossly larger carrierbeadsvvith'a surface coa'ting'of the type described above in connectionwith FIG. 1. The carrier beads serve both to maintain the fine tonerparticles deagglomerated and to charge them when the materials aretumbled together in the developing system by virtue of the relativepositions of the toner and carrier materials in the triboelectricseries. Since the carrier beads and toner particles acquire charge ofopposite polarity, the toner particles tend to cling to the carrierbeads after triboelectric charging has taken place. By changing eitherthe coating on the carrier beads or the material from which the tonerparticles are fabricated so that the toner particles are moved frombelow, the carrier beadcoating material to above this material in thetriboelectric series, the polarity of charge imparted. to thetonerparticles by this frictional charging may be reversed so that thepositive toner particles may be employed to develop a negatively chargedimage on the imaging surface 11 or negatively charged toner particlesmay be employed to develop a positively charged image. Alternatively,the toner particles may be charged to the same polarity as the polarityof the image on the imaging surface 11 so that the toner particles willbe repelled by these charged areas and will be deposited only uponuncharged areas thereby producing a photographic reversal image. At anyevent when toner particles and imaging surfaces are charged opposite inpolarity, the charged image areas pull toner particles off the earnerbeads when the carrier bead-toner particles developing mixture iscascaded over this surface. The carrier beads along with any tonerparticles not used in developingthe image then fall back into the bottomtrough of container 21 and the developed image continues around initspath until it comes opposite a fixing unit 27 which serves to fuse orpermanently fix the toner image to the imaging surface. In this case aresistance type radiant heating unit is illustrated as this type of unithas proved to be most effective in fixing toner particles includingthermoplastic materials which may be heat fused to the imaging surface11; however, other techniques known in the art may be utilized includingthe subjection of the toner image to a solvent vapor or the spraying ofthe toner image with an adhesive overcoating.

What is claimed is:

1. The method of forming a visible image comprising exposing an imagingsheet having at least a surface layer of an ultraviolet lightphotopolymerizable material to an imagewise exposure with ultravioletlight of sufficient intensity to cause polymerization of at least thesurface of said photopolymerizable material, bringing said imagewisepolymerized surface into frictional contact wlth a materal remote in thetriboelectric series from at least one of the polymerized and theunpolymerized portions of said imaging sheet so that a differentialcharge pattern is set up between image and non-image areas on said sheetand developing said charge surface by depositing finely divided,colored, electroscopic marking particles thereon.

2. The method according to claim 1 in which said photopolymerizablematerial is polyethylene terep'hthalate.

3. A method according to claim 1 in which said photopolymerizablematerial includes the cinnamate esters of polyvinyl alcohol and ofcellulose.

4. The method according to claim -1 in which said photopolymerizablematerial is 1,4-bis methyl cyclohexane polyterephthalate.

5. T he method of forming a latent electrostatic image on an imaginglayer comprisingincreasing the molecular weight of atleast a surfaceof-said layer by subjecting it to, a polymerizing influencein imagewiseconfiguration thereby modifying the triboelectric chargingsusceptibility of said surfacein imagewise configurationand bringingsaid surface into frictional contact with a ma terial remote ;-in thetriboelectricv series from atleast one of the. modified and theunmodified portions of said surfaceso that (a differential chargepattern is*set.up between image and non-image areas on said surface. t.6. A method offorming a latent electrostatic image on an imaging layercomprising coating asurface of said layer with a contaminant comprisinga material selected from the group consisting of an oil based ink andhuman body oils in imagewise configuration thereby modifying thetriboelectric charging susceptibility of said surface in imagewiseconfiguration and bringing said surface into frictional contact with amaterial remote in the triboelectric series from at least one of themodified and unmodified portitons of said surface so that a differentialcharge pattern is set up between image and non-image areas of saidsurface.

7. The method of reproducing a page of copy formed with an oil based inkcomprising placing said page of copy in face to face relationship withan imaging surface, heating at least the inked portions of said page ofcopy until at least a portion transfers across to, said imaging surfacein imagewise configuration by volatilization and condensation of atleast one of the ink components which is capable of modifying thetriboelectric charging susceptibility of said imageing surface,separating said imaging surface from said page of copy, bringin saidimaging surface into frictional contact with a material remote in thetriboelectric series from at least the ink coated portion of saidimaging surface or the noncoated portion of said imaging surface so thata differential charge pattern is set up between image and nonimage areason said imaging surface and developing said surface by depositing finelydivided, colored, electroscopic marking particles thereon.

8. A method according to claim 7 in which said page of copy is rightreading and said imaging surface is transparent whereby the mirrorreversed image produced on said imaging surface may be easily readthrough its back.

9. The method of reproducing a page of copy formed with an oil based inkcomprising placing said'page of copy in face to face relationship with asmooth surfaced impervious master sheet, heating said page of copy andsaid master sheet until at least a portion of the ink from said page ofcopy volatilizes and recondenses on said master sheet in imagewiseconfiguration, separating said master sheet and said page of copy,placing said master sheet in face to face relationship with an imagingsurface, heating said master sheet and said imaging surface until atleast a portion of the ink on said master surface volatilizes andrecondenses on said imaging surface in imagewise configuration,separating said master sheet from said imaging surface, bringing saidimaging surface into frictional contact with a material remote in thetriboelectric series from at least one of the ink coated and theuncoated portions of said imaging surface so that a differential chargepattern is set up between image and non-image areas on said imagingsurface and developing said surface by depositing finely divided,colored, electroscopic marking particles thereon.

10. A method according to claim 9 in which said original page copy isright reading and said imaging surface is transparent whereby the mirrorreversed image produced on said imaging surface may be easily readthrough its back.

11. The method of forming a reproduction of a page of copy formed withan oil based ink comprising placing said page of copy in face to facerelationship with an imaging surface, pressing the two surfaces togetherwith if s-ufficieht force to transfer at' least a portion of the inkfromi's'aid pagelofcopy-to said-imaging" 'su'rfaceg separat' ing'saidpage of"'copy- -from said imaging l surface, "bringingsaidimagin'g' surface into frictibnal'contact with amaterial-:re'mote-inthef-triboelectric series from at least one OfatheinkLcQatedand the uncoated portions of said imaging surface so that ad'ifferential char'ge'pattern "is set up btweenimage' a'nd' non-imagearea-s on -sa'id i'mag ing surfaee and devloping' said' surface 'bydepositing finelydivided, 1 'electroscopie marking 1 particles thereon;v r a 7% 1 21x12; The method 0f"-1 eproduc1ng an= image? on a" sheet ofcopy :foimed" awith an" oil" based: ink comprising placin saidcopy-sheet inface 'to face relation Witha -smo'oth surfaced-mastersheet; applying sufiicient pressure'to'said sheets so that at least aportion of the ink is transferred to said master, separating saidmasterfrom said sheet ofcopy, bringing said master into face to facecontact with an imaging surface, applying sufficient pressure to saidmaster and said imaging surface so that at least a portion of said inktransferred to said master is retransferred to said imaging surface inimagewise configuration, separating said imaging surface from saidmaster, bringing said imaging surface into frictional contactwith amaterial remote in the triboelectric series from at least one of the inkcoated and' the non-coated portionsaof said imaging surface so that adifferential charge pattern is set up between image and non-image 12a'reas"on;said imaging Lsurfaceanii developing said surfabe' bydepositing' finely Tdivided, colored; electroscopic marking-particlesthe'reon'.. I

v i I References Cited 'Q'UNITED STATES PATENTS Schwartz 96-1. 1

